Maize chlorotic dwarf virus and resistance thereto

Abstract

Methods and materials are provided to isolate the coat protein genes from maize chlorotic dwarf virus. One or more of these genes (MCDV-CP1, MCDV-CP2 or MCDV-CP3) is then incorporated in an expression cassette designed for suitable expression in a plant cell system. The resulting transformation vector is then introduced into maize to provide cross-protection to MCDV or related viral infections.

What is claimed is: 
     
       1. A DNA clone coding substantially solely for a coat protein of maize chlorotic dwarf virus. 
     
     
       2. An expression cassette comprising a DNA clone according to claim 1, operably linked to plant regulatory sequences which cause the expression of the DNA clone in plant cells. 
     
     
       3. An expression cassette comprising a DNA clone according to claim 1, operably linked to bacterial expression regulatory sequences which cause the expression of the DNA clone in bacterial cells. 
     
     
       4. Bacterial cells containing as a foreign plasmid at least one copy of an expression cassette according to claim 3. 
     
     
       5. Transformed plant cells containing as foreign DNA at least one copy of the DNA sequence of an expression cassette according to claim 2. 
     
     
       6. Transformed cells according to claim 5, further characterized in being cells of a monocotyledonous species. 
     
     
       7. Transformed cells according to claim 6, further characterized in being maize, sorghum, wheat or rice cells. 
     
     
       8. Transformed cells according to claim 5, further characterized in being cells of a dicotyledonous species. 
     
     
       9. Transformed cells according to claim 8, further characterized in being soybean, alfalfa, tobacco or tomato cells. 
     
     
       10. A maize cell or tissue culture comprising cells according to claim 7. 
     
     
       11. A transformed maize plant, the cells of which contain as foreign DNA at least one copy of the DNA sequence of an expression cassette according to claim 2. 
     
     
       12. A method of imparting resistance to maize chlorotic dwarf virus and maize dwarf mosaic virus-A to plants of a MCDV or MDMV-A susceptible taxon, comprising the steps of: a) culturing cells or tissues from at least one plant from the taxon,   b) introducing into the cells of the cell culture or tissue culture at least one copy of an expression cassette comprising a DNA clone from the RNA genome of MCDV which codes substantially solely for the coat protein of the virus, operably linked to plant regulatory sequences which cause the expression of the DNA clone in the cells, and   c) regenerating MCDV-resistant whole plants from the cell culture or tissue culture.   
     
     
       13. A method according to claim 12 which comprises the further step of sexually or clonally reproducing the whole plants in such manner that at least one copy of the sequence provided by the expression cassette is present in the cells of progeny of the reproduction. 
     
     
       14. A method according to claim 12 in which the expression cassette is introduced into the cells by electroporation. 
     
     
       15. A method according to claim 12 in which the expression cassette is introduced into the cells by microparticle bombardment. 
     
     
       16. A method according to claim 12 in which the expression cassette is introduced into the cells by microinjection. 
     
     
       17. A method according to claim 13 for providing MCDV and MDMV-A resistance in Agrobacterium tumefaciens-susceptible dicotyledonous plants in which the expression cassette is introduced into the cells by infecting the cells with Agrobacterium tumefaciens, a plasmid of which has been modified to include the expression cassette. 
     
     
       18. A method of imparting resistance to maize chlorotic dwarf virus and maize dwarf mosaic virus strain A to plants of a MCDV or MDMV-A susceptible taxon, comprising the steps of: a) selecting a fertile, MCDV resistant plant prepared by the method of claim 12 from a sexually compatible taxon;   b) sexually crossing the MCDV resistant plant with a plant from the MCDV susceptible taxon;   c) recovering reproductive material from the progeny of the cross; and   d) growing resistant plants from the reproductive material.   
     
     
       19. A method according to claim 18 which comprises the further steps of repetitively: a) backcrossing the MCDV resistant progeny with MCDV susceptible plants from the susceptible taxon; and   b) selecting for expression of MCDV resistance among the progeny of the backcross, until the desired percentage of the characteristics of the susceptible taxon are present in the progeny along with MCDV resistance.     
     
     
       20. A DNA molecule coding for maize chlorotic dwarf virus or a portion thereof which is capable of conferring resistance to maize chlorotic dwarf virus when expressed in a plant cell.